The use of large cloth bags to transport bulk quantities of powdered or granular materials, bags which can be lifted and moved by forklift trucks and other material handling equipment having hooks or tines, has become commonplace. The cloth for the bags is usually woven of strong plastic fibers, though natural fibers can also be employed. Bulk transport bags of this general type are disclosed in Nattrass et al U.S. Pat. Nos. 3,961,655 and 4,010,784 and in Sandeman et al U.S. Pat. No. 4,207,937. An improved construction for mounting lifting loops on bulk transport bags of this kind is disclosed in the co-pending U.S. patent application Ser. No. 159,833 of P. J. Nattrass filed June 16, 1980.
One persistent problem in the use of these bulk transport bags has to do with the discharge of the bulk material from a bag once it has reached its destination. To avoid the necessity of turning the bags upside-down to discharge their contents, the bags have sometimes been provided with bottom discharge openings which, of course, must be closed when the bag is in use.
Perhaps the most commonly used discharge closure arrangement is that shown in FIGS. 13-18 of the aforementioned Nattrass et al U.S. Pat. No. 3,961,655. That particular closure, however, has the disadvantage that the closure projects outwardly of the bottom wall of the bag and may be damaged by careless handling of the bag during use, with resultant loss of part or all of the bag contents. A flat closure for a bottom discharge opening in a bulk material transport bag is shown in FIGS. 1-12 of the same patent, but that closure relies upon a loose flap that may be displaced when the bag is filled so that the closure is not fully effective. Furthermore, that closure arrangement also has loose ties projecting outwardly of the bottom wall of the bag so that the closure could be accidentally opened at the wrong time.
The problem to which the present invention is directed, therefore, is the provision of a new and improved discharge closure for a bulk material transport bag that is secure against accidental opening while the bag is in use and that is essentially flat with the bottom of the bag so that the closure is protected against damage during use.
In those instances in which the top of a bulk material transport bag must be closed, similar problems appear. Thus, it is highly desirable to have the top of the bag sewn in place. Any closure for a fill opening in the top of such a bag presents the same difficulties as a bottom closure used to discharge the contents of the bag. Moreover, for both top and bottom closures, it is highly desirable that the closure preclude discharge of dust from the interior of the bag, for effective environmental control, in addition to preventing entry of fine materials that might contaminate the bag contents.